Four channel stereophonic broadcasting system

ABSTRACT

A broadcasting system wherein a left front, a right front, a left rear, and a right rear signal are transmitted on a single radio frequency channel with no significant increase in bandwidth. It should be compatible, that is, it should give satisfactory monophonic and two channel stereophonic reception on receivers presently in use by the public.

United States Patent Takaoka FOUR CHANNEL STEREOPHONIC BROADCASTINGSYSTEM [75] Inventor: Saburo Takaoka,l(ohoku-ku,

Yokohama-shi, Kanagawa, Japan [73] Assignee: Pioneer ElectronicCorporation, Tokyo, Japan [22] Filed: Nov. 9, 1971 [21] Appl. No.:196,932

[30] Foreign Application Priority Data Nov. 9, 1970 Japan 45/9851'3 [52]US. Cl. 179/15 RT [51] Int. Cl. H0411 5/00 [58] Field of Search 179/1GQ, 15 BT [56] References Cited UNITED STATES PATENTS 3,708,623 1/1973Dorren 179/15 BT (LF-LRl [451 Aug. 21, 1973 7/1972 Halpem 179/15 BTOTHER PUBLICATIONS The Quart Broadcasting System, Geryon Audio Magazine,Sept. 1970.

Quadrasonics On The Air, Feldman Audio Magazine, Jan. 1970.

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas D'AmicoAttorney-Richard C. Sughrue et a1.

[57] ABSTRACT A broadcasting system wherein a left front, a right front,a left rear, and a right rear signal are transmitted on a single radiofrequency channel with no significant increase in bandwidth. It shouldbe compatible, that is, it should give satisfactory monophonic and twochannel stereophonic reception on receivers presently in use by thepublic.

7 Claims, 2 Drawing Figures D CARRIER SUPPRESSED AM SIGNAL AT l9KHz(FREQUENCY OFA PILOT SIGNAL) A CARRIER SUPPRESSED AM SIGNAL AT 38 KHz(DOUBEED FREQUENCY l* [EM MODULATION OF EilOKHz AT 85.5KHz

FREQUENCY Hz V FM MOD FREQUENCY Hz FOUR CHANNEL STEREOPHONICBROADCASTING SYSTEM BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates to systems for the transmission ofmultiplex signals and particularly to systems for the transmission offour channel stereophonic signals by means of frequency modulationbroadcasting, and to transmitters and receivers for use in such systems.

2. Description of the Prior Art The FM multiplex stereophonicbroadcasting system, which has been adopted in Japan and is called thepilot tone system, transmits a left (or L) channel signal and a right(or R) channel signal on a single radio frequency channel and convertsthe signals with a receiver into L and R signals to achieve two channelstereophonic reproduction. On the other hand, there have been recentlydeveloped magnetic tapes and record discs having recorded thereon leftfront and right front signals in addition to left rear and right rearsignals; consequently, a system for four channel stereophonicbroadcasting is now demanded.

The main factors which are desirable in such a four channel system canbe summarized as follows: it should be compatible, that is, it shouldgive'satisfactory monophonic and two channel stereophonic reception onreceivers presently in use by the public; it should give quality equalto present systems in frequency characteristic, distortion factor,signal-to-noise ratio and other characteristics; and it should becapable of transmission of a composite signal on about 100 KHZ or lesswith no significant increase in bandwidth.

SUMMARY OF THE INVENTION It is one object of the present invention toprovide a novel and improved four channel stereophonic broadcastingsystem which is compatible with the present FM broadcasting system.

It is another object of the present invention to provide a four channelstereophonic broadcasting system which is equal in quality to thepresent system in frequency characteristic, distortion factor,signal-to-noise ratio and other characteristics.

It is a further object of the present invention to provide a fourchannel stereophonic broadcasting system in which a composite signal canbe trans-mitted on about 100 KHZ or less with no significant increase inbandwidth.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electrical block diagramof a preferred embodiment of a transmitter in accordance with theinvention, and also graphical represen-tations of frequencyrelationships of signals used in carrying out the invention.

FIG. 2 is an electrical block diagram of a preferred embodiment of areceiver in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The system of the invention willnow be described with reference to the drawings. In FIG. 1, a signalsource 1 1 produces a signal representing a left front (or LP) channel,a signal representing a right front (or RF) channel, a signalrepresenting a left rear (or LR) channel and a signal representing aright rear (or RR) channel. As indicated schematically in FIG. 1, thesesignals are added or subtracted to obtain an (LF LR) signal, an (RF RR)signal, an (LF LR) signal and an (RF RR) signal. Further, these signalsare added or subtracted to obtain an (LF LR) (RF RR) signal (hereinafterbeing called only A" signal for simplicity), an (LF LR) (RF RR) signal(3" signal), an (LF LR) (RF RR) signal (C signal) and an (LF LR) (RF RR)signal (D signal).

The A signal is positioned as a main channel signal corresponding to themain signal (L R) of the present FM multiplex broadcasting system. The8" signal, after being converted into a carrier suppressed AM signalwherein the frequency of the carrier is 38 KHZ or a doubled l9 KHZ pilotsignal, is positioned as a first subchannel signal corresponding to thesubsignal (L R) sin an of the present FM multiplex broadcasting systern.

The C signal and the D signal are converted in the same manner, that is,the C signal is positioned as a main channel signal (30 Hz 9 KHZ)corresponding to the A signal, and the D signal is positioned as asubchannel signal (10 KHZ 28 KHZ) corresponding to the B signal afterbeing converted into a carrier suppressed AM signal wherein thefrequency of the carrier is 19 KHZ which is the same as that of thepilot signal. The C signal and the D signal which are positioned in afrequencyspectrum are positioned as a second sub-channel (57.5 KHZ 113.5KHZ) higher than the first sub-channel (23 KHz 53 KHZ), after beingfrequency modulated into 85.5 KHZ 10 KHz. As is well known only onesideband of the 85.5Khz carrier need be transmitted.

By the above converting process, the A, B, C" and D signals areconverted and positioned as shown in the lower part of FIG. 1, furthermodulated into a frequency modulated signal by the frequency being usedin a present FM stereo broadcasting system at present, and thentransmitted.

Now, the receiving system of this invention will be described withreference to FIG. 2. A receiving antenna 21, an FM tuner 22 and a stereodecoder 23 are shown in a dotted line 24 and are the same as those in FMstereo receivers presently in use by the public. Therefore, the (LF LR)signal and the (RF RR) signal are led out from the output terminals ofthe stereo decoder 23.

One part of the output power of the FM tuner 22 is fed into an FMdemodulator 25 for the second subchannel and is further frequencydemodulated to produce an output signal containing the C signal and theD signal. The output signal of the FM demodulator 2-5 is fed into astereo decoder 26 for the second subchannel to be converted into the (LFLR) signal and the (RF RR) signal by the pilot signal which is suppliedfrom the stereo decoder 23 and then the two converted signals are ledout from output terminals of the decoder 26.

The (LF LR) signal and the (LF LR) signal are fed into a matrix circuit27 and are added and subtracted to produce the LF signal and the LRsignal on the two output terminals of the matrix circuit 27. The (RF RR)signal and the (RF RR) signal are fed into a matrix circuit 28 and areadded and subtracted to produce the RF signal and the RR signal on thetwo output terminals of the matrix circuit 28.

The received signal may be discriminated whether it is a monaural signalor a stereophonic signal by using the pilot signal being led out fromthe FM tuner 22, as in a prior art receiver. Furthermore, the receivedsignal may be discriminated whether it is a two channel stereophonicsignal or a four channel stereophonic signal by using the l9 KHz pilotsignal being led out from the FM demodulator 25. Therefore, an automaticswitching operation may be easily obtained so as to compose areproduction circuit corresponding to either a monaural, two channelstereophonic or four channel stereophonic signal.

The present invention has many improvements, as described hereinabove.First, compatibility can be obtained, that is, the invention givessatisfactory monophonic or two channel stereophonic reception onreceivers presently in use by the public. in other words, if a monauralreceiver receives the four channel stereophonic signal of the presentinvention, the mixed signal (LF LR RF RR) can be reproduced; and, if atwo channel stereophonic receiver receives the four channel signal, theleft signal (LF LR) and the right signal (RF RR) are reproduced.

On the other hand, if the receiver of the invention receives a monauralsignal, the monaural signal is reproduced by the front left and rightand the rear left and right speakers; and, if the receiver of theinvention receives a twochannel stereophonic signal, the left signal ofthe stereophonic signal is reproduced by the front and rear speakers ofthe left side, and the right signal is reproduced by the front and rearspeakers of the right side. In these cases, it is, of course, unnaturalthat the same signal is heard from both front and rear speakers;however, it is easy to cut off the rear signals so as to eliminate theunnatural sound by using the pilot signal, the second sub-carrier ofother suitable signals.

Second, the four signals, that is, the front and the rear signals of theleft side and those of the right side are equal to each other in theirqualities, and it is easy to get more than 30 db in channel separationbetween each channel.

Third, if the modulation degree of the main channel and the-firstsub-channel is set at less than 40 percent, and that of the pilot signaland the second sub-channel is set at less than 10 percent, the system ofthe invention is capable of transmission on a present signalradie-frequency channel with no interference between neighboringradio-frequency channels.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

1 claim:

1. A four channel stereophonic composite signal broadcasting systemcomprising a transmitter and at least one receiver, said transmittercomprising:

a. sources of left front (LF), right front (RF), left rear (LR) andright rear (RR) stereophonically related audio frequency signals,

b. means for adding the audio frequency signals together to obtain firstintermediate signals including an (LF LR) signal and an (RF RR) signal,

0. means for subtracting said audio frequency signals one from the otherto obtain second intermediate signals including an (LF LR) signal and an(RF RR) signal,

d. means for adding said first and second intermediate signals to obtainan [(LF LR) (RF RR)] or A signal and an [(LF LR) (RF RR)] or C signal,

e. means for subtracting said first and second intermediate signals onefrom the other to obtain an [(LF LR) (RF RR)] or B signal and an {(LFLR) (RF RR)]or D" signal,

f. means for supressed carrier amplitude modulating the 8 signal on acarrier of 38 R112 producing a bandwidth of 23Khz-5Khz,

g. means for suppressed carrier amplitude modulating the D signal on acarrier of I9Khz producing a bandwidth of IOKhz-ZSKhz,

h. means for combining the C signal and the modulated D signal toproduce a first composite signal in which the C signal occupies abandwidth of 30hz-9Khz and the modulated D signal occupies a bandwidthof 10Khz-28Khz,

i. means producing a pilot signal at l9Khz,

j. means for-frequency modulating said first composite signal on acarrier of 85.5Khz i lOKhz producing a bandwidth of 57.5Khz-1 13.5Khz,

it. means for combining said A signal, said pilot signal, said modulatedB signal, and said frequency modulated first composite signal to producea second composite signal in which said A signal occupies thebandwidth30hz-l5Khz, said modulated B signal occupies the bandwidth 23Khz-53Khz,and said'modulated first composite signal occupies the bandwidth57.5Khz-l 13.5Khz,

1. means for frequency modulating said second composite signal, and

m. means for broadcasting said frequency modulated second compositesignal.

2. A broadcasting system as defined in claim 1 wherein said one receivercomprises:

a. a first FM demodulator circuit for demodulating the received FMsecond composite signal,

b. a first stereo decoder for obtaining an (LF LR) signal and an (RF RR)signal by using the output signal of said first FM demodulator circuitand a pilot signal, 1

c. a second FM demodulator circuit for further demodulating the signalcoming from the first FM de-' modulator circuit,

d. a second stereo decoder for obtaining an (LF LR) signal and an (RFRR) signal by using the output signal of the second FM demodulatorcircuit and the pilot signal, and

e. matrix circuit means for combining said (LF LR), (RF RR), (LF LR) and(RF RR) signals to obtain LF, LR, RF and RR signals.

3. A four channel st'ereophonic composite signal broadcasting systemincluding a transmitter comprisa. sources of left front (LF), rightfront (RF), left rear (LR) and right rear (RR) stereophonically relatedaudio frequency signals,

b. means for adding the audio frequency signals together to obtain firstintermediate signals including an (LF LR) signal and an (RF RR) signal,

0. means for subtracting said audio frequency signals one from the otherto obtain second intermediate ma M... A.

signals including an (LF LR) signal and an (RF RR) signal,

d. means for adding said first and second intermedi ate signals toobtain an [(LF LR) (RF RR)] or A signal and an [(LF LR) (RF RR)] or Csignal,

e. means for subtracting said first and second intermediate signals onefrom the other to obtain an [(LF LR) (RF RR)] or B signal and an [(LFLR) (RF RR)] or D" signal,

. means for supressed carrier amplitude modulating the B signal on acarrier of 38 Khz producing a bandwidth of 23Khz-53Khz,

g. means for suppressed carrier amplitude modulating the D signal on acarrier of 19Khz producing a bandwidth of lOKhz28Khz,

h. means for combining the C signal and the modulated D signal toproduce a first composite signal in which the C signal occupies abandwidth of 30hz-9Khz and the modulated D signal occupies a bandwidthof lOKhz-28Khz,

i. means for producing a pilot signal at 19Khz,

j. means for frequency modulating said first compos' ite signal on acarrier of 85.5KhzilOKhz producing a bandwidth of 57.5Khzl 13.5Khz,

k. means for combining said A signal, said pilot signal, said modulatedB signal, and said frequency modulated first composite signal to producea second composite signal in which said A signal occupies the bandwidth30hz-15Khz, said modulated B signal occupies the bandwidth 23Khz-53Khz,and said modulated first composite signal occupies the bandwidth57.5Khz-l 13.5Khz,

1. means for frequency modulating said second composite signal, and

in. means for broadcasting said frequency modulated second compositesignal.

4. A receiver for receiving the broadcast frequency modulated signalformed in accordance with claim 3, said receiver comprising a. a firstFM demodulator circuit for demodulating the recieved FM second compositesignal,

b. a first stereo decoder for obtaining an (LF LR) signal and an (RF RR)signal by using the output signal of said first FM demodulator circuitand the pilot signal,

c. a second FM demodulator circuit for further demodulating the signalcoming from the first FM demodulator circuit,

d. a second stereo decoder for obtaining an (LF LR) signal and an (RFRR) signal by using the output signal of the second FM demodulatorcircuit and the pilot signal, and

e. matrix circuit means for combining said (LF LR), (RF+ RR), (LF LR)and (RF RR) signals to obtain LF, LR, RF and RR signals.

5. A method of broadcasting a four channel stereophonic composite signalcomprising the steps of a. generating left front (LF), right front (RF),left rear (LR) and right rear (RR) stereophonically related audiofrequency signals,

b. adding the audio frequency signals together to obtain firstintermediate signals including an (LF LR) signal and an (RF RR) signal,

0. subtracting said audio frequency signals one from the other to obtainsecond intermediate signals including an (LF LR) signal and an (RF RR)signal,

. adding said first and second intermediate signals to obtain an [(LFLR) (RF RR)] or A signal and an [(LF LR) (RF RR)] or C" signal,

. subtracting said first and second intermediate signals one from theother to obtain an [(LF LR) (RF RR)] or B signal and an [(LF LR) (RFRR)} or 13" signal,

f. suppressed carrier amplitude modulating the B signal on a carrier of38Khz producing a bandwidth of 23Khz-53Khz,

g. suppressed carrier amplitude modulating the D signal on a carrier ofl9Khz producing a bandwidth of l0Kh2-28Khz,

. combining the C signal and the modulated D signal to produce a firstcomposite signal in which the C signal occupies a bandwidth of 30hz-9Khzand the modulated D signal occupies a bandwidth of IOKhz-28Khz,

. producing a pilot signal at 19Khz,

. frequency modulating said first composite signal on a carrier of85.5Khz lOKhz producing a bandwidth of 57.5Khzl13.5l(hz,

k. combining said A signal, said pilot signal, said modulated B signal,and said modulated first composite signal to produce a second compositesignal in which said A signal occupies the bandwidth 30hz-l5Khz, saidmodulated B signal occupies the bandwidth 23Khz-53Khz, and saidmodulated first composite signal occupies the bandwidth 57.5Khz-l13.5Khz,

1. frequency modulating said second composite signal, and

in. broadcasting said frequency modulated second composite signal.

6. A method as defined in claim 5, further comprising receiving thebroadcast FM composite signal by:

a. frequency-demodulating the received FM second composite signal toobtain a first output signal,

b. decoding the first output signal with the pilot signal to obtain an(LF LR) signal and an (RF RR) signal,

c. further demodulating the first output signal to produce a secondoutput signal,

(1. decoding the second output signal with the pilot signal to obtain an(LF LR) signal and an (RF RR) signal, and

e. combining said (LF LR), (RF RR), (LF 4 LR) and (RF RR) signals toreproduce the LF, LR, RF and RR signals.

7. A method of receiving the broadcast FM composite signal formed inaccordance with the method of claim 5 and comprising:

a. frequency-demodulating the received FM second composite signal toobtain a first output signal,

b. decoding the first output signal with the pilot signal to obtain an(LF LR) signal and an (RF RR) signal,

c. further demodulating the first output signal to produce a secondoutput signal,

d. decoding the second output signal with the pilot signal to obtain an(LF' LR) signal and an (RF RR) signal, and

e. combining said (LF LR), (RF RR), (LF LR) and (RF RR) signals toreproduce the LF, LR, RF and RR signals.

1. A four channel stereophonic composite signal broadcasting systemcomprising a transmitter and at least one receiver, said transmittercomprising: a. sources of left front (LF), right front (RF), left rear(LR) and right rear (RR) stereophonically related audio frequencysignals, b. means for adding the audio frequency signals together toobtain first intermediate signals including an (LF + LR) signal and an(RF + RR) signal, c. means for subtracting said audio frequency signalsone from the other to obtain second intermediate signals including an(LF - LR) signal and an (RF - RR) signal, d. means for adding said firstand second intermediate signals to obtain an ((LF + LR) + (RF + RR)) or''''A'''' signal and an ((LF - LR) + (RF - RR)) or ''''C'''' signal, e.means for subtracting said first and second intermediate signals onefrom the other to obtain an ((LF + LR) - (RF + RR)) or ''''B'''' signaland an ((LF - LR) - (RF - RR))or ''''D'''' signal, f. means forsupressed carrier amplitude modulating the B signal on a carrier of 38Khz producing a bandwidth of 23Khz-5Khz, g. means for suppressed carrieramplitude modulating the D signal on a carrier of 19Khz producing abandwidth of 10Khz28Khz, h. means for combining the C signal and themodulated D signal to produce a first composite signal in which the Csignal occupies a bandwidth of 30hz-9Khz and the modulated D signaloccupies a bandwidth of 10Khz-28Khz, i. means producing a pilot signalat 19Khz, j. means for frequency modulating said first composite signalon a carrier of 85.5Khz + OR - 10Khz producing a bandwidth of57.5Khz-113.5Khz, k. means for combining said A signal, said pilotsignal, said modulated B signal, and said frequency modulated firstcomposite signal to produce a second composite signal in which said Asignal occupies the bandwidth 30hz-15Khz, said modulated B signaloccupies the bandwidth 23Khz-53Khz, and said modulated first compositesignal occupies the bandwidth 57.5Khz-113.5Khz, l. means for frequencymodulating said second composite signal, and m. means for broadcastingsaid frequency modulated second composite signal.
 2. A broadcastingsystem as defined in claim 1 wherein said one receiver comprises: a. afirst FM demodulator circuit for demodulating the received FM secondcomposite signal, b. a first stereo decoder for obtaining an (LF + LR)signal and an (RF + RR) signal by using the output signal of said firstFM demodulator circuit and a pilot signal, c. a second FM demodulatorcircuit for further demodulating the signal coming from the first FMdemodulator circuit, d. a second stereo decoder for obtaining an (LF -LR) signal and an (RF - RR) signal by using the output signal of thesecond FM demodulator circuit and the pilot signal, and e. matrixcircuit means for combining said (LF + LR), (RF + RR), (LF - LR) and(RF - RR) signals to obtain LF, LR, RF and RR signals.
 3. A four channelstereophonic composite signal broadcasting system including atransmitter comprising: a. sources of left front (LF), right front (RF),left rear (LR) and right rear (RR) stereophonically related audiofrequency signals, b. means for adding the audio frequency signalstogether to obtain first intermediate signals including an (LF + LR)signal and an (RF + RR) signal, c. means for subtracting said audiofrequency signals one from the other to obtain second intermediatesignals including an (LF - LR) signal and an (RF - RR) signal, d. meansfor adding said first and second intermediate signals to obtain an((LF + LR) + (RF + RR)) or ''''A'''' signal and an ((LF - LR) + (RF -RR)) or ''''C'''' signal, e. means for subtracting said first and secondintermediate signals one from the other to obtain an ((LF + LR) - (RF +RR)) or ''''B'''' signal and an ((LF - LR) - (RF - RR)) or ''''D''''signal, f. means for supressed carrier amplitude modulating the B signalon a carrier of 38 Khz producing a bandwidth of 23Khz-53Khz, g. meansfor suppressed carrier amplitude modulating the D signal on a carrier of19Khz producing a bandwidth of 10Khz-28Khz, h. means for combining the Csignal and the modulated D signal to produce a first composite signal inwhich the C signal occupies a bandwidth of 30hz-9Khz and the modulated Dsignal occupies a bandwidth of 10Khz-28Khz, i. means for producing apilot signal at 19Khz, j. means for frequency modulating said firstcomposite signal on a carrier of 85.5Khz + or - 10Khz producing abandwidth of 57.5Khz-113.5Khz, k. means for combining said A signal,said pilot signal, said modulated B signal, and said frequency modulatedfirst composite signal to produce a second composite signal in whichsaid A signal occupies the bandwidth 30hz-15Khz, said modulated B signaloccupies the bandwidth 23Khz-53Khz, and said modulated first compositesignal occupies the bandwidth 57.5Khz-113.5Khz, l. means for frequencymodulating said second composite signal, and m. means for broadcastingsaid frequency modulated second composite signal.
 4. A receiver forreceiving the broadcast frequency modulated signal formed in accordancewith claim 3, said receiver comprising a. a first FM demodulator circuitfor demodulating the recieved FM second composite signal, b. a firststereo decoder for obtaining an (LF + LR) signal and an (RF + RR) signalby using the output signal of said first FM demodulator circuit and thepilot signal, c. a second FM demodulator circuit for furtherdemodulating the signal coming from the first FM demodulator circuit, d.a second stereo decoder for obtaining an (LF - LR) signal and an (RF -RR) signal by using the output signal of the second FM demodulatorcircuit and the pilot signal, and e. matrix circuit means for combiningsaid (LF + LR), (RF + RR), (LF - LR) and (RF - RR) signals to obtain LF,LR, RF and RR signals.
 5. A method of broadcasting a four channelstereophonic composite signal comprising the steps of a. generating leftfront (LF), right front (RF), left rear (LR) and right rear (RR)stereophonically related audio frequency signals, b. adding the audiofrequency signals together to obtain first intermediate signalsincluding an (LF + LR) signal and an (RF + RR) signal, c. subtractingsaid audio frequency signals one from the other to obtain secondintermediate signals including an (LF - LR) signal and an (RF - RR)signal, d. adding said first and second intermediate signals to obtainan ((LF + LR) + (RF + RR)) or ''''A'''' signal and an ((LF - LR) + (RF -RR)) or ''''C'''' signal, e. subtracting said first and secondintermediate signals one from the other to obtain an ((LF + LR) - (RF +RR)) or ''''B'''' signal and an ((LF - LR) - (RF - RR)) or ''''D''''signal, f. suppressed carrier amplitude modulating the B signal on acarrier of 38Khz producing a bandwidth of 23Khz-53Khz, g. suppressedcarrier amplitude modulating the D signal on a carrier of 19Khzproducing a bandwidth of 10Khz-28Khz, h. combining the C signal and themodulated D signal to produce a first composite signal in which the Csignal occupies a bandwidth of 30hz-9Khz and the modulated D signaloccupies a bandwidth of 10Khz-28Khz, i. producing a pilot signal at19Khz, j. frequency modulating said first composite signal on a carrierof 85.5Khz + or - 10Khz producing a bandwidth of 57.5Khz-113.5Khz, k.combining said A signal, said pilot signal, said modulated B signal, andsaid modulated first composite signal to produce a second compositesignal in which said A signal occupies the bandwidth 30hz-15Khz, saidmodulated B signal occupies the bandwidth 23Khz-53Khz, and saidmodulated first composite signal occupies the bandwidth57.5Khz-113.5Khz, l. frequency modulating said second composite signal,and m. broadcasting said frequency modulated second composite signal. 6.A method as defined in claim 5, further comprising receiving thebroadcast FM composite signal by: a. frequency-demodulating the receivedFM second compOsite signal to obtain a first output signal, b. decodingthe first output signal with the pilot signal to obtain an (LF + LR)signal and an (RF + RR) signal, c. further demodulating the first outputsignal to produce a second output signal, d. decoding the second outputsignal with the pilot signal to obtain an (LF - LR) signal and an (RF -RR) signal, and e. combining said (LF + LR), (RF + RR), (LF - LR) and(RF - RR) signals to reproduce the LF, LR, RF and RR signals.
 7. Amethod of receiving the broadcast FM composite signal formed inaccordance with the method of claim 5 and comprising: a.frequency-demodulating the received FM second composite signal to obtaina first output signal, b. decoding the first output signal with thepilot signal to obtain an (LF + LR) signal and an (RF + RR) signal, c.further demodulating the first output signal to produce a second outputsignal, d. decoding the second output signal with the pilot signal toobtain an (LF - LR) signal and an (RF - RR) signal, and e. combiningsaid (LF + LR), (RF + RR), (LF - LR) and (RF - RR) signals to reproducethe LF, LR, RF and RR signals.